Weights of various types are commonly used to anchor pipelines, particularly for pipelines running through water bodies, marshes, sloughs, or other moisture-laden zones in which pipelines might be upwardly displaced due to buoyancy forces. Bag-type pipeline weights are typically made from a flexible and durable fabric or similar material, with pockets or compartments that can be filled with ballast material (such as gravel) to provide weight as needed. The filled weights are then laid over or attached to a pipeline at spaced intervals. Some known bag-type weights incorporate or require straps of some sort, to be wrapped and tied around the pipeline. Other designs simply rely on the ballast mass to keep the weights in place relative to the pipeline. Some known designs are configured to straddle the pipeline, with ballast-filled side lobes extending down each side of the pipeline. Bag-type weights have a particular advantage over other known pipeline weights in that they can be filled with ballast material at or near to a pipeline-laying operation, resulting in considerably lower weight transportation costs as compared to, for instance, precast concrete weights.
Examples of prior art bag-type pipeline weights may be found in the following patent documents: U.S. Pat. No. 3,793,845 (Keith); CA 2,075,006 and U.S. Pat. No. 5,385,430 (Connors); and CA 2,277,523 and U.S. Pat. No. 6,220,788 (Jewell).
The problem of providing ballast for larger diameter pipelines (e.g., 16-inch plus) has particular challenges. The volume of a pipe per unit of pipe length (i.e., the cross-sectional area of the pipe) is proportionate to the square of the diameter. Accordingly, the potential buoyancy forces acting on a pipeline, per unit of pipeline length, also vary with the square of the pipeline diameter, and the ballast weight (or anchoring force) required to counteract the potential buoyancy forces is generally proportional to the square of the pipeline diameter as well. For example, the ballast weight required to weigh down a given length of 32-inch diameter pipeline will be about four times greater than for the same length of 16-inch diameter pipe (in similar service conditions).
Because of their inherent configurations, prior art bag-type weights are not suitable or readily adaptable for ballasting large-diameter pipe. For example, weights such as those taught by Jewell are not readily scalable to accommodate the much greater mass of ballast required for large-diameter pipelines. The Connors design, if scaled up to hold greatly increased amounts of ballast, will be difficult to fill, handle, and install, particularly where it is desired or necessary to install a pipeline in a trench with minimum possible side clearances.
For the foregoing reasons, there is a need for a bag-type pipeline weight design that is readily adaptable to accommodate the large volumes of gravel or other ballast material required to weigh down large-diameter pipelines. At the same time, there is a need for a bag-type pipeline weight for large-diameter pipelines that is easier to fill, transport, and install than known bag-type weight designs. Furthermore, there is a need for a bag-type pipeline weight for large-diameter pipelines that substantially retains its shape after being filled with ballast and during installation, thus facilitating its use in comparatively narrow pipeline trenches. The present invention is directed to these needs.